Ignition apparatus for a plasma burner

ABSTRACT

A safe, convenient ignition arrangement is described for a &#39;&#39;&#39;&#39;cold&#39;&#39;&#39;&#39; plasma burner adapted, e.g., to effect a finishing surface-hardening operation on a grounded metallic workpiece. Argon or other plasma-forming gas is subjected to an electromagnetic field in an elongated ionization chamber. The resulting ionized gas passes through a working gap formed between an output nozzle of the conductive chamber and an elongated electrode mounted axially in the chamber. A remotely located switch is operative to complete an electrical path to ground through the gap and the electrode, thereby igniting the ionized gas.

United States Patent Rainer 1 Oct. 29, 1974 1 i IGNITION APPARATUS FOR A PLASMA 3,353,061 11/1967 Davis 315 111 BURNER 3,50l,675 3/1970 Cleaver ct 3l3/23l X [75] Inventor: Rudolf Rainer, Kapfenberg, Austria {73] Assignee: Gebr. Bohler & Co. AG, Vienna,

Austria [22l Filed: Sept. 10, 1973 [Zll App]. No: 395,412

|3U| Foreign Application Priority Data Sept, 8, I972 Austria 7700/72 |52| US. Cl. 313/231, 315/1 ll [5 [1 Int. Cl. H01] 7/30 [58] Field ofSearch 3l5/lll;3l3/23l; 333/99 PL [56] References Cited UNITED STATES PATENTS 3192.427 6/1965 Sugawara ct a] 3lS/l ll X Primary ExaminerPaul L. Gensler [57] ABSTRACT A safe, convenient ignition arrangement is described for a cold" plasma burner adapted, e.g.. to effect a finishing surface-hardening operation on a grounded metallic workpiece. Argon or other plasma-forming gas is subjected to an electromagnetic field in an elongated ionization chamber. The resulting ionized gas passes through a working gap formed between an output nozzle of the conductive chamber and an elongated electrode mounted axially in the chamber. A remotely located switch is operative to complete an electrical path to ground through the gap and the electrode, thereby igniting the ionized gas.

2 Claims, 2 Drawing Figures PAIENTEDnm 29 I974 SEEIIUF 2 or 3 h T I IGNITION APPARATUS FOR A PLASMA BURNER BACKGROUND OF THE INVENTION One advantageous way of providing a surfacehardening operation on a metallic workpiece is to subject the affected surface to a burning stream of cold plasma", (Le, a gas that has been ionized by highfrequency electromagnetic energy rather than by an electric arc). The gas stream is directed downwardly out of a nozzle of a conductive ionization chamber that is placed above and adjacent to the affected surface of the workpiece, which is grounded. Ignition of such gas stream is accomplished by completing an electrical path to ground through the ionized gas via the conductive nozzle in the presence of the electromagnetic field.

In the past, the completion of the electrical path for ignition purposes was accomplished by having an operation manually pass a conductive pin through the nozzle while the path is live. Such procedure is not only clumsy and inconvenient since such manual operation must take place in they vicinity of the burner-workpiece interface, but more important it is dangerous, since it can subject the operator to severe electrical shock and burns.

SUMMARY OF THE INVENTION These disadvantages may be overcome with the cold plasma ignition system in accordance with the invention.

In an illustrative embodiment, an elongated electrode extends downwardly through the elongated ionization chamber of the burner in insulating relation with the chamber walls. The lowermost tip of the electrode terminates within the chamber adjacent the output nozzle to define a working gap therebetween.

A high-speed switch is operative to ground the electrode to complete the ignition effecting electrical path through the working gap. A manual actuator for the switch may be conveniently located remote from the interface between the burner and the workpiece.

BRIEF DESCRIPTION OF THE DRAWING The invention will be further set forth in the following detailed description taken in conjunction with the appended drawing, in which:

FIG. I is a pictorial diagram illustrating, in an overall arrangement for applying a cold plasma flame to a grounded workpiece, a flame ignition circuit in accordance with the invention; and

FIG. 2 is an elevational view in section of a plasma burner useful in the arrangement of FIG. 1, showing certain details of the ignition facilities in the burner.

DETAILED DESCRIPTION Referring now to FIG. I, a grounded conductive workpiece 14 formed, e.g., from hardenable steel, is subjected to a surface hardening operation by exposure to a flaming stream of cold plasma passed downwardly from a conductive output nozzle 2 ofa plasma burner l.

The surface layer (designated 20) of the workpiece to be hardened is exposed to said flaming stream of cold plasma (as for example described in copending and coassigned application Ser. No. [82,420, filed Sept. 2|, 1971), so that a surface layer is formed by rapid heating and cooling. As is known, for instance, from the coassigned US. Pat. No. 3,6l5,924, the introduction of further energy, such as a mechanical shock converts such layer into a very hard and tough martensite layer.

The burner I employed for this purpose includes an electrically conductive elongated chamber l8 which converges at its lower end in the nozzle 2. A plasmaforming gas such as argon is introduced into a gas port 3 near the upper end of the chamber from a suitable gas supply 13. Such gas may be ionized into a cold plasma within the chamber by high frequency electromagnetic energy coupled to the chamber from a suitable generator 12 via an input connection 6. The generator 12 is selectively excitable from a power supply 15 by means of a manually operated switch II.

In order to ignite the cold plasma into a flaming stream for application to the workpiece 14, an electric path to ground is established through the gas to commence an are. In accordance with the invention, such path is provided for in a safe and accessible manner by suitably mounting and selectively grounding an elongated electrode 5 within the chamber l8 in insulating relation with the chamber walls.

As shown more clearly in the illustrative arrangement of FIG. 2, the electrode 5 extends downwardly into the chamber 18 through a central bore 21 of an insulating sleeve 4. The sleeve is disposed coaxially within the chamber 18. A lower end 22 of the electrode 5 extends beyond the lower end of the bore 21 and terminates adjacent the nozzle 2 to define a working gap 23 within the chamber. An upper end 19 ofthe electrode 5 is disposed in communication with a grounding switch 9 through a coupling 7 and an ignition cable 8.

Referring again to FIG. 1, the switch 9 includes a contact assembly 9A interconnecting the ignition cable 8 to ground. The assembly 9A is operable when a coil 9B of the switch is excited. Such excitation, in turn, is accomplished by coupling a suitable voltage source across the coil 98 via a manual switch 10 (e.g., a push button.) Depression of the push button 10 is effective to ignite the ionized gas in the chamber 18 by grounding the electrode 5 and thereby completing an electric path to ground through the gas via the working gap 23 (FIG. 2).

The ignition arrangement just described is highly advantageous in that it eliminates the danger of electric shock on burns to the operator, who in previous arrangements had to manually insert a metallic pin into the nozzle to start the arc. Moreover, the described arrangement is convenient in that the only part of such arrangement requiring manual attention by the opera tor is the push button 10, which of course can be located in an accessible location remote from the nozzle workpiece interface.

The electrode 5 is illustratively made of Tungsten, although it may also consist of any of the material having high temperature stability and good electron emission characteristics.

Because of the rapidity at which the ignition arc may form in the presence of the high frequency field from the generator 12, the switch 9 may be as a highfrequency circuit breaker or other high-speed device.

In the foregoing, the invention has been described in the form of an illustrative embodiment. Many variations and modifications will now be evident to those skilled in the art. It is accordingly desired that the scope of the appended claims not be limited to the specific disclosure herein contained.

What is claimed is:

1. ln a plasma burner apparatus including an elongated, electrically conductive chamber for ionizing a plasmaforming gas by subjecting the gas to an electromagnetic field and for igniting the ionized gas by completing an electrical path to ground through the ionized gas via an output nozzle at the lower end of the chaml0 ber, an improved arrangement for igniting the ionized gas, which comprises:

an elongated electrode extending longitudinally downward through the chamber in spaced relation tending beyond the lower end of the bore. 

1. In a plasma burner apparatus including an elongated, electrically conductive chamber for ionizing a plasma- forming gas by subjecting the gas to an electromagnetic field and for igniting the ionized gas by completing an electrical path to ground through the ionized gas via an output nozzle at the lower end of the chamber, an improved arrangement for igniting the ionized gas, which comprises: an elongated elecTrode extending longitudinally downward through the chamber in spaced relation with the chamber walls, the lower end of the electrode terminating within the chamber adjacent the output nozzle to form a working gap; and switching means associated with the chamber and operable to ground the electrode to complete the electrical path through the working gap.
 2. An arrangement as defined in claim 1, in which the burner apparatus includes an insulating sleeve extending longitudinally downward through the chamber and having a central bore, the electrode being disposed in the central bore with the lower end of the electrode extending beyond the lower end of the bore. 